The present invention relates to an improved magnetooptic recording material, and more particularly relates to improvement in corrosion resistance of a Tb-Fe-Co type material used for magnetooptic discs suited for high density recording.
A magnetooptic disc is in general made up of a substrate and a thin film of magnetooptic material formed on the substrate in an arrangement such that its easy magnetization axis is perpendicular to the surface of the substrate. The thin film has a uniform magnetization direction.
At writing-in of signals, laser is applied to a portion of the thin film of a magnetooptic disc to raise its temperature up to near the Curie point, reverse weak magnetic field is applied to the portion under this condition by a magnetic head to reverse the magnetization direction of the heated portion and the heated portion is cooled down to the room temperature. Kerr effect is utilized in reading-out of signals from a magnetooptic disc. Polarized laser is applied to the thin film of the disc and difference in intensity of the reflective ray is detected, the difference being caused by difference in Kerr rotation angle (.theta.k) of the plane of polarization. Signals read out are removed from recording
Among various magnetic materials used for such magnetooptic discs, Tb-Fe-Co type magnetic material has won much recognitions. Such increasing use of this alloy is caused by the fact that the Curie point of this alloy is as low as 200.degree. C. and magnetic reversion can be effected very easily. Since its coersive force (Hc) is about 240 kA/m, the alloy does not allow easy magnetic reversion at the room temperature, thereby assuring high recording stability. It is also easy with this alloy to enhance recording density of the magnetooptic disc.
Despite these advantages, Tb-Fe-Co type magnetooptic material is very vulnerable to corrosion due to inclusion of easily oxidizable Tb. Although additional inclusion of Al and/or Ti has been proposed, no satisfactory effects has ever been obtained.